Hello,
Here are the reasons for color changes in gold fish. It could be that the fish has been kept indoors and without full sunlight or some form of UVB light. Fish that are suffering from pigment loss in the skin are usually Orange Comets or Red Caps which are famous for turning white. The key to helping your fish is:
1) Check water quality
2)Make sure the discolored or white areas are not raised as compared to the other skin
3) Make sure discolored or white areas are not recessed under the rest of the skin or scales
4)Fish is acting well, eating normally, and fins are erect and white .
If all this is correct I would try adding a UVB light to the area where the fish are kept. Joan Jav917
Veterinary Technician
I am Vet Tech. for 30+yrs. who works with all animals. I do alot of rescue work with small animals.